Genetic control of cell functions is being studied by isolation and analysis of mutants that are defective in some aspect of conjugation or related processes controlled by mating-type. Mutants are isolated as sterile, unable to produce alpha-factor, or unable to respond to alpha- factor. They are characterized with respect to their ability to mate at normal frequencies, produce appropriate sex factors, respond to sex factors, mate at low frequency, and, in diploids, to sporulate. They are further analyzed by tetrad or random spore analysis for linkage relationships to the mating-type locus. The results are intended to develop an understanding of the genetic control system regulating these functions.